Device for rotatably positioning a camera or similar article about two orthogonal axes

ABSTRACT

A positioning device is provided for rotatably positioning a camera or other article about orthogonal rotational axes. The positioning device includes a carriage supported for rotation about a horizontal axis by a yoke. The yoke is in turn rotatably coupled to a base assembly for rotation of the yoke about a vertical axis. Rotation of the camera about the horizontal and vertical axes is respectively effected by first and second voice coil actuators, each comprising a pair of magnets and at least one coil to which current is supplied. The amplitude and direction of the current supplied to the coil determines the speed and direction of rotation of the camera. The second voice coil actuator preferably includes a coil assembly comprising two opposed coils. This design overcomes the angular range limitations associated with prior art voice coil actuators and enables rotation of the camera about an extended angular range. The device can be advantageously utilized for adjustment of the pan and tilt angles of a video camera in a conferencing system.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.60/089,009, filed on Jun. 11, 1998 and entitled “Two-Axis PositioningDevice”.

BACKGROUND

1. Field of the Invention

The present invention relates generally to positioning devices, and moreparticularly to a device for rotatably positioning a camera about twoorthogonal rotational axes.

2. Description of the Prior Art

Videoconferencing systems utilize video cameras to capture an image ofthe conference participants for transmission to a remote conferencingsite. The video camera may be beneficially provided with a device foradjusting the rotational orientation of the camera such that the imageof a speaking conference participant is properly framed. The rotationalorientation of the camera may be adjusted manually by user manipulationof controls (located either on a videoconferencing system console or ona remote control device associated therewith) which cause the camera torotate in the desired direction or directions. Alternatively andpreferably, adjustment of the camera's rotational orientation isachieved by an automatic technique such as acoustic localization,wherein the position of the speaking participant is calculated byanalysis of plural acoustic signals, and the camera is steered in thedirection of the calculated position.

Irrespective of whether the camera rotational positioning device iscontrolled by manual or automatic techniques, such devices require oneor more actuators to rotate the camera such that the desired rotationalorientation is achieved. Positioning devices designed to rotate thecamera about two orthogonal axes (in order to enable more accurateframing of the image of speaking conference participants) typicallyutilize two actuators: the first actuator rotates the camera about avertical axis, while the second actuator rotates the camera about ahorizontal axis perpendicular to the camera's longitudinal axis.Rotation of the camera about the vertical axis is referred to herein as“panning”; rotation about the horizontal axis is referred to herein as“tilting”; and, devices for rotating the camera about a vertical andhorizontal axis are referred to herein as “pan/tilt positioningdevices.”

Most presently-employed pan/tilt positioning devices utilize steppermotors to effect rotation of the camera. Stepper motors have theadvantage of being relatively inexpensive, easy to control, and widelycommercially available in a range of sizes and operationalspecifications. However, the use of stepper motors to rotate a camera ina videoconferencing system has a number of problems associatedtherewith. Typically, a gear train or similar set of transmissionelements must be employed to transmit power from the stepper motor shaftto the camera. Movement of the gears during operation of the positioningdevice can generate a substantial amount of noise. This noise can beannoying and distracting to the conference participants. Moreimportantly, the noise can interfere with acoustic localizationtechniques utilized to automatically orient the camera in the directionof the speaking participant.

Further, gears or other transmission elements may be susceptible tomisalignment or breakage due to wear or rough handling, therebyrendering the positioning device partially or fully inoperative. Stillfurther, the inclusion of the gear train into the positioning devicemakes its assembly more complex and consequently raises manufacturingcosts. Finally, positioning devices utilizing stepper motors typicallyoperate slowly and/or have limited angular resolution.

In view of the foregoing discussion, there is a need for a rotationalpositioning device which operates substantially noiselessly, does notrequire a gear train or similar to transmit power from the actuators tothe camera.

SUMMARY

The present invention comprises a rotational positioning device for acamera or similar article which utilizes voice coil actuators to driverotation of the camera about first and second orthogonal rotationalaxes. The positioning device includes a carriage to which the camera isfixedly attached. The carriage is supported by a yoke such that it canpivot relative to the yoke about a horizontal axis orthogonal to thelongitudinal axis of the camera (thereby allowing adjustment of thecamera's tilt angle). The yoke is in turn coupled to a base for pivotalmovement relative to the base about a vertical axis (thereby allowingadjustment of the pan angle).

The positioning device advantageously employs first and secondrotational actuators of the voice-coil type to respectively effecttilting and panning movements of the camera. As is known in the art, thevoice coil actuators each include a set of permanent magnets and atleast one coil wound on a non-ferrous base. Supplying current to thecoil alters a magnetic field generated in a gap disposed between themagnets and the coil, thereby creating a force vector and causing themagnets to move relative to the coil (or the coil to move relative tothe magnets, depending on whether the coil or the magnets are free tomove). In a preferred embodiment of the invention, the first voice coilactuator is configured to tilt the camera, and comprises a verticallyoriented coil, mounted to the yoke, interposed between a pair of returnplates depending from the carriage. One of the return plates is providedwith a pair of arcuate permanent magnets. When current is supplied tothe coil, the carriage and supported camera are caused to rotate (tilt)relative to the yoke. The direction and speed of rotation is controlledby varying the direction and amount of current supplied to the coil.

In order to overcome rotational travel limitations associated withconventional rotational voice coil actuators, the second rotationalactuator is preferably adapted with a dual-coil design. This designadvantageously enables panning of the camera about an extended angularrange (up to a full 360°). The second voice coil actuator preferablycomprises a planar coil assembly supporting two opposed coils. The coilassembly is centrally mounted to a depending shaft of the yoke forco-rotation therewith, and is disposed in a gap between a base plate anda return plate of the base assembly. A pair of adjacently positionedarcuate permanent magnets are fastened to an underside of the returnplate. Panning of the camera is effected by supplying current to thecoils of the coil assembly, which causes the coil assembly and yoke torotate relative to the base assembly. By appropriate commutation of thecurrent supplied to the two coils, the camera may be panned over anextended angular range.

The positioning device may be further provided with a control system forprecise control of the pan and tilt angle of the camera. The controlsystem comprises a processor, a set of current supplies each configuredto supply current to one coil of the first or second voice coilactuator, and angular position sensors for continuously detecting thepan and tilt angle of the camera. The processor is configured tocalculate the desired pan and tilt angles of the camera based onacoustic localization data or the like and to determine the differencebetween the present pan and tilt angles (as measured by the angularposition sensors). The, processor then directs each of the currentsupplies to supply current to the actuator coils so as to cause thepositioning device to move the camera to the desired orientation.

BRIEF DESCRIPTION OF THE FIGURES

In the accompanying figures:

FIG. 1 is a front isometric view of a positioning device according tothe present invention;

FIG. 2 is a front elevated view of the positioning device;

FIG. 3 is a rear isometric view of the positioning device;

FIG. 4 is an elevated side view depicting components of a tiltingactuator of the positioning device;

FIG. 5 is a top plan view depicting components of a panning actuator ofthe positioning device;

FIG. 6 is an isometric view of the components of the panning actuator;

FIG. 7 is an isometric view of a coil assembly of the panning actuator;and

FIG. 8 is a schematic depiction of an exemplary control system for thecamera positioning device.

DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

The present invention provides a positioning device for positioning avideo camera or similar article about two orthogonal rotational axes.The following description is intended to enable one skilled in the artto make and use the invention, and is provided in the context of apatent application and its requirements.

FIGS. 1-3 are, respectively, front perspective, front elevated, and rearperspective views of a positioning device 100 according to a preferredembodiment of the present invention. A video camera 102 or similararticle: is mechanically coupled to positioning device 100 to enablepositioning of camera 102 about vertical (pan) and horizontal (tilt)rotational axes. Camera 102 is fixedly mounted to a carriage 104 formovement therewith. Carriage 104 is rotatably mounted to a yoke 106 topermit rotation of carriage 104 and camera 102 relative to yoke 106about a horizontal axis generally perpendicular to an optical axis ofcamera 102 (thereby permitting tilting of camera 102). Yoke 106 is inturn rotatably mounted to a base assembly 108 for rotation relative tobase assembly 108 about a vertical axis. The carriage 104 and camera 102co-rotate with yoke 106 about the vertical axis to produce panning ofcamera 102. As is discussed in detail hereinbelow, tilting and panningof camera 102 are respectively effected by operation of first and secondvoice coil actuators 110 and 112, each comprising a pair of permanentmagnets and at least one coil to which current is selectively applied togenerate a torque vector.

Carriage 104 is provided with opposed shafts 114 a and 114 b or similarelements which define the tilt axis. Shafts 114 a and 114 b arerespectively supported in bearings 116 a and 116 b disposed in yoke 106to permit tilting movement of camera 102 relative to yoke 106. One ormore counterweights (not shown) may be secured to carriage 104 tobalance carriage 104 and camera 102 within yoke 106 and thereby reduceactuator 110 torque load. As is discussed in further detail below inconnection with FIG. 8, positioning device 100 may be provided with anangular position sensor 117 associated with shaft 114 a for continuouslymeasuring a tilt angle of camera 102.

Base assembly 108 comprises generally planar return plate 118 and baseplate 120 held in parallel spaced apart relation by spacers 122. Returnplate 118 and base plate 120 are preferably fabricated from low-carboncold-rolled steel or a suitable equivalent. Base assembly 108 isprovided with bearing 124 which supports a central shaft 126 dependingfrom yoke 106 such that yoke 106 may rotate about a vertical axisrelative to base assembly 108 to effect panning movement of camera 102.A second angular position sensor 128, mechanically associated with shaft126, functions to continuously measure a pan angle of camera 102.

Tilting and panning movement of camera 102 are respectively driven byfirst and second voice coil actuators 110 and 112. The operationalprinciples of voice coil motors are well known in the art and need notbe discussed in detail herein. Generally, a voice coil actuatorcomprises at least one coil positioned in spaced apart relation to atleast one permanent magnet. By selectively supplying current to the coiland thereby generating an associated magnetic field, the permanentmagnet is caused to move relative to the coil (or the coil is caused tomove relative to the permanent magnet). Voice coil actuators may beconfigured to produce linear or rotational movement (as in the presentinvention). The speed and direction of movement are controlled byvarying the amount and direction of current supplied to the coil.

Referring in particular to FIGS. 2 and 4, first (tilt) voice coilactuator 110 is seen to comprise coil 130 (depicted in phantom in FIG.4) interposed between first and second return plates 132 and 134, whichdepend from carriage 104. First and second return plates 132 and 134 areattached to or formed integrally with carriage 104, and are fabricatedfrom steel or suitable equivalent to provide a magnetic return path forfirst voice coil actuator 110. Arcuate permanent magnets 136 and 138 arefastened to return plate 132 and are adjacently positioned along thecircumference of a circle having its center located at the horizontalaxis of rotation of positioning device 100. Magnets 136 and 138preferably comprise high energy product rare earth magnets (such asneodymium-iron-boron magnets), and are configured such thatcorresponding faces of magnets 136 and 138 possess the same magneticpolarities, i.e., both of the outwardly directed faces comprise thenorth (or south) poles, and both of the, inwardly directed facescomprise south (or north) poles.

Coil 130, typically comprising copper windings supported on anon-ferrous base, is mounted in bracket 140 secured to a lowerhorizontal portion of yoke 106 and extends vertically upward into a gapdefined between first and second return plates 132 and 134. The leads(not shown) of coil 130 are connected to a current source.

To effect a tilting movement of camera 102, current is supplied to coil130 to thereby generate a magnetic field in the gap between coil 130 andmagnets 136 and 138. The magnetic field thus generated applies a forceto magnets 136 and 138, causing carriage 104 and camera 102 to rotaterelative to yoke 106 about the horizontal or tilt axis. The speed anddirection of rotation (i.e., whether camera 102 is tilted upwardly ordownwardly) is achieved by adjusting the direction and magnitude of thecurrent supplied to coil 130.

Panning of camera 102 (rotation about the vertical axis) is achieved byoperation of second voice coil actuator 112. Those skilled in the artwill recognize that conventional single-coil voice coil actuators havelimited angular travel (typically around 20 degrees). To overcome thislimitation, the present invention utilizes a multi-coil design whichadvantageously enables panning of camera 102 about an extended angularrange (up to a full 360°).

Referring to FIGS. 2 and 5-6, second voice coil actuator 112 includes acoil assembly 142 fixedly attached to depending yoke shaft 126 forco-rotation therewith. The generally planar voice coil assembly 142 isdisposed in a gap defined interiorly of base plate 120 and return plate118. As may best be seen with reference to FIG. 7, coil assembly 142 isgenerally circular in shape, and comprises a coil housing 144 whichsupports in opposed laterally spaced relation first and second coils 146and 148. Base plate 120, in addition to having a structural function,also acts as a magnetic flux return path for second voice coil actuator112. Coil housing 144 is preferably fabricated from molded plastic orother non-conductive material. First and second coils 146 and 148 eachtypically comprise copper windings on a non-ferrous base, and each coilis provided with a pair of leads (not shown) for connection to a currentsource.

Returning to FIGS. 5-7, arcuate permanent magnets 150 and 152 arefastened to the underside of return plate 118 and are positioned inadjacent relation along a circumference of a circle having its centerlocated at the vertical axis of rotation of yoke 106 and camera 102.Magnets 150 and 152 preferably comprise high energy product rare earthmagnets (such as neodymium-iron-boron magnets), and are configured (in amanner similar to magnets 136 and 138 of first or tilt voice coilactuator 110) such that corresponding faces of magnets 150 possess thesame magnetic polarities, i.e., both of the upwardly directed facescomprise the north (or south) poles, and both of the downwardly directedfaces comprise south (or north) poles.

When current is supplied to one or both of coils 146 and 148, theresulting magnetic field causes a rotational force to be applied to coilassembly 142, in turn producing rotation of yoke 106 and camera 102about the vertical or panning axis. Again, the speed and direction ofrotation of camera 102 is determined by the amount and direction ofcurrent supplied to coils 146 and 148. By appropriately commutatingcurrent supplied to coils 146 and 148, second or panning voice coilactuator 112 may be operated over an extended angular range, thusenabling camera 102 to be oriented toward any participant located withinthe room in which the conference is being held.

It is to be appreciated that panning actuator 112 is configured suchthat coil assembly 142 rotates while return plate 118 and magnets 150and 152 are static. Because magnets 150 and 152 are considerably moremassive than coil assembly 142, this “static magnet” arrangement servesto reduce the inertia of the moving portions of panning actuator 112,thereby reducing torque requirements and permitting more rapid panningof camera 102.

FIG. 6 depicts in block form an exemplary control system 200 forcontrolling the operation of positioning device 100. As is discussedhereinabove, positioning device 100 may be advantageously utilized toproperly frame the image of a speaking participant in a groupvideoconference setting. In practice, camera 102 will be maintained at aconstant pan and tilt angle while a first participant is speaking from afixed location (note that the tilt angle may be defined as the angulardisplacement of the camera from a perfectly horizontal orientation, andpan angle may be defined as the angular displacement of the camera aboutthe vertical axis from a “straight-ahead” orientation). When a secondparticipant begins to speak (or when the first participant moves fromthe fixed location), control system 200 causes positioning device 100 torotate camera 102 about the horizontal and vertical (tilt and pan) axesuntil camera 102 is oriented to new pan and tilt angles appropriate forframing the image of the second speaking participant (or the movingfirst speaking participant).

As depicted in FIG. 6, control system 200 comprises a camera positionprocessor 202; current sources 204, 206 and 208, each for supplying adesired amount of current to a corresponding coil 130, 146 or 148; firstangular position sensor 117 for continuously measuring a present tiltangle of camera 102; and, second angular position sensor 128 forcontinuously measuring the present pan angle of 102 camera. Cameraposition processor 202 is configured to calculate target pan and tiltangles which will properly frame the image of the speaking participant.Camera position processor 202 may utilize any suitable technique tolocate the speaker and determine the target pan and tilt angles foraiming the camera, such as triangularization based on analysis ofacoustic signals received by plural spaced-apart microphones. Once thetarget pan and tilt angles are determined, camera position processor 202directs current sources 204, 206 and 208 to supply current to thecorresponding coils such that camera 200 is moved in the direction ofthe target pan and tilt angles.

The camera's present pan and tilt angles are continuously detected byfirst and second angular position sensors 117 and 128. Sensors 117 and128 may comprise conventional optical angular encoders or mayalternatively comprise the cross-polarization polarization detectorsdescribed in co-assigned U.S. patent application Ser. No. 09/179,104,filed on Oct. 26, 1998 and entitled “System and Method for Measuring theAngular Position of a Rotatably Positionable Object”. Sensors 117 and128 sense the angular positions of associated shafts 114 a and 126, andresponsively generate signals for transmission to camera positionprocessor 202, which in turn calculates the difference between thepresent and target pan and tilt angles and causes the current suppliedto coils 130, 146 and 148 to be adjusted accordingly. Once the desiredpan and tilt angles are attained, the current supplied to each coil 130,146 and 148 is adjusted so that camera 102 remains static (noting that asmall amount of current may need to be supplied to one or more coils toprevent camera 102 from being displaced from the target pan and tiltangles due to the influence of gravity). As described above, the targetpan and tilt angles are periodically recalculated to allow camera 102 tobe oriented to a newly speaking participant or to track a movingspeaker.

Those skilled in the art will recognize that various features disclosedin connection with the preferred embodiment may be used eitherindividually or jointly. For example, a positioning device may beprovided with two dual-coil actuators to enable orientation of thesupported article about two extended angular ranges. Further, thepresent invention is intended to include positioning devices whichrotatably position an article about a single axis, but which utilize thetwo-coil actuator described hereinabove to overcome the angular strokelimitations associated with prior art voice coil actuators.

It is to be further appreciated that while the positioning apparatus ofthe present invention has been described with reference to a preferredimplementation thereof, i.e., a video camera positioning device, theinvention is not limited thereto. Those having ordinary skill in the artwill recognize that the present invention may be beneficially utilizedin any number of environments and implementations. Accordingly, theclaims set forth below should be construed in view of the full breadthand spirit of the invention as disclosed herein.

What is claimed is:
 1. A rotational positioning device for a cameracomprising: a yoke for rotatably supporting the camera, the camera beingrotatable relative to the yoke about a first rotational axis; a firstvoice coil actuator for causing the article to rotate about the firstrotational axis; a base assembly, mechanically coupled to the yoke, theyoke being rotatable relative to the base about a second rotational axisorthogonal to the first rotational axis; and a second voice coilactuator for causing the yoke and the supported article to rotate aboutthe second rotational axis, the second voice coil actuator comprising agenerally planar coil assembly comprising at least two coils to whichcurrent may be independently supplied and being fixedly coupled to theyoke for co-rotation therewith, and a set of concentrically arrangedpermanent magnets fixedly attached to the base assembly; whereby thecamera may be positioned about the first and second rotational axes byadjusting current supplied to the first and second voice coil actuators.2. The positioning device of claim 1, wherein the camera is a videocamera, the first rotational axis is a substantially horizontal axisperpendicular to an optical axis of the video camera, and the secondrotational axis is a substantially vertical axis.
 3. The positioningdevice of claim 1, further comprising a control system for controllingpositioning of the camera about the first and second rotational axes. 4.The positioning device of claim 3, wherein the control system furthercomprises: a set of sensors for continuously generating signalsrepresentative of the angular position of the camera; at least oneprocessor, coupled to the set of sensors, for receiving the signals andresponsively adjusting the current supplied to the first and secondvoice coil actuators such that the camera is caused to rotate in thedirection of a desired angular position.
 5. A rotational positioningdevice for a camera comprising: means for supporting the camera, thecamera being rotatable relative to the supporting means about a firstrotational axis; a first voice coil actuator for causing the camera torotate about the first rotational axis; a base, mechanically coupled tothe supporting means such that the supporting means and the camera arerotatable relative to the base about a second rotational axis orthogonalto the first rotational axis; and a second voice coil actuator forcausing the camera and supporting means to rotate relative to the base,the second voice coil actuator including a voice coil assembly fixedlycoupled to one of the supporting means or the base for co-rotationtherewith, and a set of permanent magnets fixedly coupled to the otherof the supporting means or the base; whereby the camera may bepositioned about the first and second rotational axes by adjustingcurrent supplied to the first and second voice coil actuators.
 6. Thedevice of claim 5, further including means for controlling an angularposition of the camera.
 7. The device of claim 6, wherein the means forcontrolling further comprises: angular position sensing means fordetecting the angular position of the camera and responsively generatingangular position signals; processing means, electronically coupled tothe angular position sensing means for receiving the angular positionsignals and responsively adjusting current supplied to the first andsecond voice coil actuators to move the camera in the direction of apredetermined angular position setpoint.